Perhaps the best way to understand virtual reality is to consider it in terms of the widening of the bandwidth of the interface between the computer and the user. The WIMP interface (Windows-Icons-Mice-Pulldown menus) of the Apple Macintosh was heralded because it facilitated the interactivity between the computer and the user. It was like improving your axe by buying a new handle rather than a new head. However, it is a very mixed metaphor - are we in a house (window), a drafting office (icon), a pet shop (mouse), or a restaurant (pulldown menu)? It turns out that we are on a desktop, with a trash can sitting on it! Whereas the WIMP interface is a good first step towards the intimate coupling of the person with the machine, it is not a true graphic interface. Imagine, however, that the computer screen opened to an image of an office. If you want to use your computer for word-processing, click on the typewriter sitting on the desk; if you want to use it as a data base management system, click on the appropriate drawer in the filing cabinet; if you want to use it as a front end to control a videodisc-player or a CD-ROM player, click on the icon representing the device on the top of your cabinet; and, if you want to throw something away, there is a waste-paper basket under the desk where it belongs. Imagine further that, with steadily improving graphic and sound capabilities, you have a high-resolution colour image of an office rather than a simple black-and-white line drawing, and that this image was expanded to fill an entire wall and then wrapped around to fill a whole room. Suppose that you could interact with this room, not by pointing to icons and pulling down menus with a mouse, but simply by pointing to representations of the various objects in your office and voicing your command. You are now in virtual reality. Alternatively, imagine that the office image was shrunk rather than expanded, and that two slightly different versions of the office image were presented in a set of goggles to your two eyes to produce a stereoscopic effect. Suppose even further that the mouse was replaced by a dataglove so that, rather than merely pointing to objects in the office, you could manipulate those objects. Welcome again to virtual reality.